OP here. My MIL and I are very close. I didn’t have a great relationship with my own mother and she has been kind of like a mother to me. We are very similar and she is super helpful. She wants to come to meet our baby and help out. She has been social distancing.

If you really trust her to have distanced correctly, yes. But that's a high bar for me.

I would do it. I think I would require her to quarantine for 2 weeks -- i.e. not go to the grocery store even, not use a public toilet on the drive, etc -- but it's totally doable. We traveled long-distance this summer via car with two kids, and we brought our own toilet and food. Just stopped for gas. It was easy to social distance.